1. Field of the Invention
The invention is directed to a torsional vibration damper.
2. Discussion of the Prior Art
A torsional vibration damper with two transmission elements which are rotatable relative to one another about a common axis of rotation is known from German reference DE 42 00 174 Al. A movement conducted to one of the transmission elements can be conducted to the other respective transmission element by means of a coupling device. The coupling device has a coupling member which is arranged at the drive-side transmission element in an articulated manner and acts on a mass via a joint. This mass connected in turn with the transmission element on the driven side in an articulated manner.
In torsional vibration dampers with a coupling device of this kind between the transmission elements in connection with a mass, the instantaneous position of the individual elements of the coupling device relative to one another substantially depends on the centrifugal force determined by the rate of rotation and on the intensity of the torsional vibrations that are introduced. The centrifugal force tends to pull the individual elements radially outward, while the torsional vibrations tend to compel a deflection in the circumferential direction from this stable middle position. The centrifugal force increases as the rate of rotation increases, so that the coupling device is perceived as having greater stiffness at a higher rate of rotation than at a low rate of rotation. Accordingly, a torsional vibration damper of this kind does not present difficulties as regards resonant frequencies and is therefore very well-suited for damping torsional vibrations which occur in motor vehicles with internal combustion engines below 1000 RPM. However, against this advantage there is the disadvantage that the coupling device itself responds relatively inertly due to the use of the individual elements in connection with a mass which are oriented under the influence of centrifugal force. Further, a coupling device of this kind is sensitive to relative wobbling movements between the two transmission elements because the wobbling movements lead to tilting in the region of the joint connecting the coupling member with the mass, resulting in wear at this joint. A further disadvantage is that the coupling member and mass can occupy two different end positions relative to one another, so that there is no clearly defined relative position between the two transmission elements.
German reference DE 36 30 398 A1 describes a torsional vibration damper which likewise has two transmission elements which are rotatable relative to one another about a common axis of rotation, but in which the coupling device is formed by springs in a working connection with the two transmission elements in order to transmit a movement conducted to one of the transmission elements. A coupling device of this kind works so as to be relatively free of inertia, but is comparatively expensive and has the considerable disadvantage that the resonant frequency of the torsional vibration damper is also predetermined by the selected spring rigidity. At determined rates of rotation in the motor vehicle containing the torsional vibration damper, this causes at least a loss of comfort but under less favorable circumstances can also lead to damage or even destruction of the torsional vibration damper.